Thermal management of laser diode mode hopping for heat assisted media recording

ABSTRACT

A method and apparatus provide for determining a temperature at a junction of a laser diode when the laser diode is operated in a lasing state that facilitates heat-assisted magnetic recording, comparing the junction temperature and an injection current supplied during the lasing state to stored combinations of junction temperature and injection current, and determining a likelihood of mode hopping occurring for the laser diode during the lasing state based on the comparison to stored combinations of junction temperature and injection current.

RELATED PATENT DOCUMENTS

This application is a continuation of U.S. Ser. No. 15/061,166, filedMar. 4, 2016, which is a continuation of U.S. Ser. No. 14/492,802, filedSep. 22, 2014, now U.S. Pat. No. 9,281,659, to which priority is claimedand which are hereby incorporated by reference in their entireties.

SUMMARY

Examples described herein include methods, apparatuses, and techniquesrelated to heat-assisted media recording (HAMR). In one embodiment, amethod includes determining a temperature at a junction of a laser diodewhen the laser diode is operated in a lasing state that facilitatesheat-assisted magnetic recording, comparing the junction temperature andan injection current supplied during the lasing state to storedcombinations of junction temperature and injection current, anddetermining a likelihood of mode hopping occurring for the laser diodeduring the lasing state based on the comparison to stored combinationsof junction temperature and injection current.

According to another embodiment, an apparatus includes a laser diode, asensor, and an analyzer. The laser diode is configured to facilitateheat assisted magnetic recording in a lasing state. The sensor isconfigured to measure a temperature of a junction of the laser diode.The analyzer is configured to determine a likelihood of mode hoppingoccurring for the laser diode during the lasing state based on acomparison of the junction temperature and an injection current of thelaser diode to stored combinations of junction temperature and injectioncurrent.

Another exemplary embodiment is directed to a method that includessupplying an injection current to a laser diode, measuring a temperatureof the junction of the laser diode when in a lasing state thatfacilitates heat-assisted magnetic recording, comparing the monitoredjunction temperature and the supplied injection current to the storedcombinations of junction temperature and injection current, determiningif the measured junction temperature and supplied injection currentcomprises a combination for which mode hopping is likely to occur basedupon the comparisons to stored combinations of junction temperature andinjection current, and implementing one or more measures to attenuatethe effects of or reduce the likelihood of mode hopping duringheat-assisted recording.

These and other features and aspects of various embodiments may beunderstood in view of the following detailed discussion and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The discussion below makes reference to the following figures, whereinthe same reference number may be used to identify the similar/samecomponent in multiple figures.

FIGS. 1-4 are flow charts illustrating processes/methods according toexample embodiments;

FIG. 5 is graph of a laser diode voltage over time at various knownsubstantially constant current levels;

FIG. 5A is a graph of laser diode voltage against injection current forthe embodiment of FIG. 5;

FIG. 5B is an enlargement of the graph of FIG. 5 showing a transitionbetween voltage states;

FIG. 6 is a schematic that includes a laser diode coupled in parallelwith a heater arrangement according to an example embodiment;

FIG. 7 is a graph of laser bias and temperature over time with andwithout heating applied thereto according to an example embodiment;

FIG. 8 is a schematic that includes a laser diode coupled in parallelwith a heater arrangement according to another example embodiment;

FIG. 9 is a graph of laser bias over time and illustrating anoscillating drive signal including a negative-going portion for forwardbiasing a heating arrangement according to an example embodiment;

FIG. 10 is a schematic view of a laser diode and a heater arrangementeach part of an independent circuit according to yet another exampleembodiment;

FIG. 11 is a flow chart of a process/method according to an exampleembodiment;

FIG. 12 is a schematic view of an apparatus and related componentsaccording to an example embodiment;

FIG. 13 is a schematic view of an apparatus and related componentsaccording to another example embodiment; and

FIG. 14 is a schematic view of an apparatus and related componentsaccording to yet another example embodiment.

DETAILED DESCRIPTION

This disclosure describes structures and techniques for mitigatingtemperature-induced mode hopping of a laser diode used in heat-assistedmagnetic recording (HAMR) devices. In particular, some embodimentsdetermine a junction temperature of the laser diode and can have aheating element that warms the junction to mitigate instances of powerinstability associated with laser diode mode hopping during HAMR. Otherembodiments determine the junction temperature of the laser diode andpredict a likelihood that mode hopping will occur. One or more measurescan be implemented based upon the prediction that mode hopping is likelyto reduce its negative impact upon HAMR.

In HAMR devices, also sometimes referred to as thermal-assisted magneticrecording (TAMR) devices or energy assisted magnetic recording (EAMR), amagnetic recording medium (e.g., hard drive disk) is able to overcomesuperparamagnetic effects that limit the areal data density of typicalmagnetic media. In a HAMR recording device, information bits arerecorded on a storage layer at elevated temperatures. The heated area inthe storage layer determines the data bit dimension, and linearrecording density is determined by the magnetic transitions between thedata bits.

In order to achieve desired data density, a HAMR recording head (e.g.,slider) includes optical components that direct light from a laser diodeto the recording media. The HAMR media hotspot may need to be smallerthan a half-wavelength of light available from current sources (e.g.,laser diodes). Due to what is known as the diffraction limit, opticalcomponents cannot focus the light at this scale. One way to achieve tinyconfined hot spots is to use an optical near field transducer (NFT),such as a plasmonic optical antenna. The NFT is designed to supportlocal surface-plasmon at a designed light wavelength. At resonance, highelectric field surrounds the NFT due to the collective oscillation ofelectrons in the metal. Part of the field will tunnel into a storagemedium and get absorbed, raising the temperature of the medium locallyfor recording. During recording, a write element (e.g., write pole)applies a magnetic field to the heated portion of the medium. The heatlowers the magnetic coercivity of the media, allowing the applied fieldto change the magnetic orientation of heated portion. The magneticorientation of the heated portion determines whether a one or a zero isrecorded. By varying the magnetic field applied to the magneticrecording medium while it is moving, data is encoded onto the medium.

A HAMR drive uses a laser diode to heat the media to aid in therecording process. Due to inefficiencies of electric to optical power,the laser diode also heats itself during lasing. Components (writer,reader, heat elements) in the magnetic slider also dissipate heat andthe heat is conducted to laser diode as the laser diode submount ismounted on the slider. These components (including the laser diode) canexperience significant heating due to light absorption andelectric-to-optical conversion inefficiencies as energy produced by thelaser diode is delivered to the magnetic recording medium (not shown).During write operation, these light absorption and inefficiencies willvary the junction temperature of the laser diode, causing a shift inlaser emission wavelength, leading to a change of optical feedback fromoptical path in slider to the cavity of the laser diode, a phenomenonthat is known to lead to mode hopping/power instability of the laserdiode. Mode hopping is particularly problematic in the context ofsingle-frequency lasers. Under some external influences, asingle-frequency laser may operate on one resonator mode (e.g., produceenergy with a first wavelength) for some time, but then suddenly switchto another mode (produce energy, often with different magnitude, with asecond wavelength) performing “mode hopping.” Temperature variation isknown to cause mode hopping in laser diodes. Some of the physicalmechanisms for thermally-induced mode hopping are thought to betemperature dependence of laser gain, index of refraction, and cavitylength.

Mode hopping is problematic for HAMR applications, as mode hopping leadsto laser output power jumping and magnetic transition shifting from oneblock of data to another. Large transition shifts in a block of datacannot be recovered in channel decoding, resulting in error bits. Thisdisclosure discusses various techniques, methods, and apparatuses thatcan be used to predict a likelihood of mode hopping occurring duringHAMR. Additionally, various techniques, methods, and apparatuses aredisclosed that can be used to mitigate the occurrence of mode hoppingand/or reduce the undesirable effects of mode hopping for HAMRapplications.

FIG. 1 illustrates an exemplary method that determines a likelihood ofmode hopping during HAMR. The method determines 101 a temperature of ajunction of a laser diode when in a lasing state that facilitates HAMR.In some instances, the method can determine the junction temperature ina non-lasing state as well as the lasing state. As will be discussed inFIGS. 2 and 3, and in reference to various subsequent FIGURES, thedetermination of the junction temperature can be made throughtemperature measurement (utilizing sensors) or calculation. The methodutilizes the measured junction temperature and a known injection currentsupplied to the laser diode during the lasing state to compare 102 themeasured junction temperature and injection current to storedcombinations of junction temperature and injection current. The storedcombinations of junction temperature and injection current will varyfrom embodiment to embodiment and are dependent upon various criteriaincluding the lasing wavelength, laser diode type, amount of opticalfeedback, operational temperatures of various components within thedrive, etc. Based upon the comparison 102 to the stored combinations ofjunction temperature and injection current, the method determines 103 alikelihood of mode hopping occurring for the laser diode during thelasing state. Optionally, one or more measures 104 can be implemented tomitigate the effects or reduce the likelihood of mode hopping duringHAMR. Some examples of these measures will be discussed in furtherdetail subsequently.

FIG. 2 illustrates another exemplary method that determines a likelihoodof mode hopping during HAMR. The method of FIG. 2 calculates 201 thetemperature of the junction of the laser diode when in a lasing statethat facilitates HAMR. In some instances, the temperature of thejunction can also be calculated in a non-lasing state. Thisdetermination can be made, for example, by a forward voltage methodduring the lasing state that is based on the relationship betweenvoltage, current, and laser diode junction temperature. Indeed, themethod is based upon the fact that voltage of a constant current islinearly proportional to the junction temperature. Laser diode injectioncurrent is a known quantity as it is controlled. Laser power output canbe measured, by for example, a laser power monitor (e.g. a photodiode)or other methods. One method of calculating the junction temperaturefrom the power output and the current will be discussed subsequently inreference to FIGS. 5 and 5A.

The method of FIG. 2 compares 202 the measured junction temperature anda known injection current supplied to the laser diode during the lasingstate to stored combinations of junction temperature and injectioncurrent. Based upon the comparison 202, the method determines 203 alikelihood of mode hopping occurring for the laser diode during thelasing state. As with the embodiment of FIG. 1, various measures 204 canbe implemented to mitigate the effects or reduce the likelihood of modehopping during HAMR.

FIG. 3 illustrates yet another exemplary method for determining alikelihood of mode hopping during HAMR. The method of FIG. 3 measures301 the temperature of the junction of the laser diode when in a lasingstate that facilitates HAMR. Measurement of the junction temperature canbe made during the non-lasing state as well. The measurement can beperformed using a sensor (e.g., a thermistor as discussed in referenceto FIG. 6). The method compares 302 the measured junction temperatureand a known injection current supplied to the laser diode during thelasing state to stored combinations of junction temperature andinjection current. Based upon the comparison 302, the method determines303 a likelihood of mode hopping occurring for the laser diode duringthe lasing state. The method specifies one of various optional measures,heating 304 the laser diode, which can be used to reduce the likelihoodof mode hopping.

FIG. 4 illustrates a flow chart of according to another method. Themethod proceeds from start 400 and monitors 402 the junction temperatureand an injection current of the laser diode during the lasing state. Themonitored junction temperature and the injection current are compared404 to stored combinations of junction temperature and injectioncurrent. In some instances, the stored data can additionally includeinformation regarding slider/head temperatures, case temperatures,magnetic recording medium temperatures, etc. that can be used with thestored injection current information. The method determines 406 if themeasured junction temperature and injection current comprises acombination for which mode hopping is likely to occur based upon thecomparisons to stored combinations of junction temperature and injectioncurrent. If mode hopping is unlikely, the method proceeds to allow thelaser diode to deliver 408 energy to the magnetic recording medium usingan appropriate injection current. However, if mode hopping is determinedto be likely, the method proceeds to implement measures 410 to mitigatethe effects or reduce the likelihood of mode hopping. These measures caninclude one or more of: heating or cooling the laser diode, adjustinglaser injection current higher or lower to avoid a combination ofjunction temperature and injection current for which mode hopping islikely to occur, temporarily stopping writing or holding operation untilthe junction temperature is reduced, preheating the laser diode byturning it on prior to writing data tracks, etc. Preheating of the laserdiode can include applying a power that is below a lasing threshold tothe laser diode if a small amount of heating of the junction is desired,or moving the head to a position where data can be overwritten andapplying a full lasing power to the laser diode if a larger amount ofheating of the junction is desired. After one or more of the measures410 has been applied, a second check 412 can be performed to determineif the measured junction temperature and injection current comprises acombination for which mode hopping is likely to occur based upon thecomparisons to stored combinations of junction temperature and injectioncurrent. If mode hopping is determined to be likely, further measures410 to mitigate the effects or reduce the likelihood of mode hopping canbe implemented. If mode hopping is determined to be unlikely, the methodproceeds to deliver energy to the magnetic recording medium 414.

Additionally, the method can be provided with redundancy or anothercheck after writing of a data sector is complete such as illustrated instep 416. Step 416 determines if a combination of junction temperatureand injection current for which mode hopping was likely to have occurredwas inadvertently crossed during energy delivery 408. In some instances,if such a combination was found to have occurred, the sector of dataaffected can be rewritten at step 408. In other instances, if acomparison of the measured junction temperature and injection current tostored combinations of junction temperature and injection currentindicates mode hopping was unlikely to have occurred, yet additionalmonitoring/analysis (e.g., optical power monitoring, review of recordeddata, laser wavelength monitoring) indicates mode hopping was likely tohave occurred, the method can proceed to recalibrate 418 the storedtemperature and injection current data to allow for a betteridentification of mode hopping based upon the measured junctiontemperature and injection current can be performed.

FIGS. 5, 5A, and 5B illustrate graphs 500, 502, and 504 that provide anexample of how the temperature of the junction of the laser diode can becalculated. This technique does not rely on sensors (e.g. thermistor)for monitoring and indeed performs no sensing during the non-lasingstate. The technique allows for determination of a junction temperatureof the laser diode in both the lasing state and the non-lasing state.The technique is based on the relationship between voltage, current, andlaser diode junction temperature (i.e., voltage at low constant (˜1 mA)current is linearly proportional to the junction temperature). Laserdiode current is a known quantity as it is controlled as illustrated inFIG. 5. Laser power output can be measured, by for example, a laserpower monitor (e.g. a photodiode), analyzing patterns in recorded datato deduce power variation, etc.

FIG. 5 provides a graph where current is increased such that laser diodevoltage increases from zero to substantially a steady state (e.g., about1.37 V) and held at this steady state for a period of time. In theembodiment of FIG. 5, the current is increased to a high current suchthat voltage is also increased. This lasing state is held at a highpower state for a period of time sufficient for junction temperature toadjust and then the current is abruptly returned to a lower currentstate (e.g. back to the 1 mA state) and held in that state for a periodof time to allow for return of a steady state voltage and an adjustmentof junction temperature.

FIG. 5A provides a graph 502 of the laser diode voltage measured againstinjection current for the embodiment described in FIG. 5. The graph 502illustrates that voltage increases rapidly from zero until a voltageassociated with the steady state (e.g., about 1.37 V) turn-on voltage isreached. Because constant current is linearly proportional to thejunction temperature, a voltage, V_(e), associated with the low currentstate can be extrapolated by fitting a linear line back from the steadystate voltage.

FIG. 5B provides an enlargement of a portion of FIG. 5 where the currentis suddenly reduced from the maximum state and then pulsed up to thelower current state. The pulse illustrated in FIG. 5B has a timeduration t in the hundreds of nanosecond in some instances. FIG. 5Billustrates that the voltage dips measurably for a transient temperatureperiod (e.g., t) before returning toward a steady state voltage providedby the constant current. In FIG. 5B, the amount of this dip ΔV=0.024 isprovided for exemplary purposes. Because voltage of a constant currentis linearly proportional to the junction temperature, the amount of ΔVprovides a measure of ΔT at the junction of the laser diode. Thetechnique involves a calibration step in which a proportionality factorK is determined. This can be accomplished by measuring forward voltagein a first state where temperature is known (e.g., at a room temperaturewhere the laser is driven by a very low known constant current, forexample, 1 mA or less as illustrated) and, for example, at a secondknown voltage state (e.g., a high voltage or zero voltage V_(e)). Thetemperatures during these voltage states can be measured by a sensor(e.g., thermistor, etc.).

The proportionality factor K can be calculated according to Equation (1)as follows:

K=(V ₁ −V ₂)/(T ₂ −T ₁)   (1)

where V₁ is the voltage measured during the first state (e.g., a roomtemperature state), V₂ is the voltage measured during the second state(e.g., a high voltage state, a zero voltage state, etc.), T₂ is thetemperature measured during the second state, and T₁ is the temperaturemeasured during the first state.

Once the proportionality factor K has been determined for the laserdiode, given a sensed ΔV, ΔT can be calculated as changes in current areknown. As illustrated in FIG. 5B, the forward voltage can be measuredbefore and after heating by a high pulsed drive current to determine ΔV.Thermal impedance (R_(Thermal Impedance)) can be calculated according toEquation (2) as:

R _(Thermal Impedance) =K̂ ⁻¹*[ΔV/P _(heat)]  (2)

where ΔV=V_(before pulse)−V_(after pulse) and P_(heat from pulse) is thepower expended during the heat pulse. The power expended during the heatpulse P_(heat from pulse) can be calculated according to Equation (3):

P _(heat from pulse)=(ΔI*ΔV)−P_(light)   (3)

where ΔI is the change in current applied during the pulse, andP_(light) is the change in lasing power measured during the pulse by,for example, a photodiode or another sensor or method. In short, theforward voltage technique described determines a voltage differentialbetween a transient voltage lasing state of the laser diode and aconstant voltage lasing state of the laser diode (as measured just priorto and just after a high pulsed drive current is applied). The forwardvoltage technique calculates the temperature differential based on thevoltage differential using the proportionality factor K and theassumption that the temperature differential between the transientvoltage lasing state and the constant voltage lasing state is relativelyminimal (i.e. and some cases can be assumed to be zero) due to therelatively slower diffusion of heat along the junction as compared withfaster response of electrical signals.

FIG. 6 is a simplified circuit arrangement 600 that electrically couplesa laser diode 602 and a heater arrangement 604 in a parallelrelationship. The heater arrangement 604 can be disposed proximate thelaser diode 602 (e.g. in, along, or adjacent thereto) and can be used toheat the laser diode 602. Indeed in some instances the spatial proximityof the heater arrangement 604 to the junction of the laser diode 602 issuch that heat can diffuse quickly (e.g., <1 μs) to the laser junctionand maintain a smaller laser junction temperature variation. Thus, insome instances the heater arrangement 604 can be positioned in or alongthe laser diode 602 itself. In other instances, the heater arrangement604 can be disposed on adjacent components such as the transducer head,etc. In the embodiment shown in FIG. 6, the heater arrangement cancomprise a diode 606 coupled in series with a heater/thermistor 608.However, in some embodiments the heater arrangement can be comprised ofonly a diode (e.g. FIG. 8). The heater/thermistor 608 can allow theheater arrangement 604 to act as a temperature sensor of the junctiontemperature of the laser diode 602 (at least during a portion of thenon-lasing state) in addition to providing heating to the junction. Insome cases, the temperature sensor can be configured to measure atemperature of the junction of the laser diode in one or both of thelasing state and the non-lasing state.

As illustrated in FIG. 6, the circuit 600 is configured to alternatelyoperate the laser diode 602 in a lasing state and a non-lasing state,and to activate the heater arrangement 604 during the non-lasing stateto warm a junction of the laser diode 602. In the embodiment of FIG. 6,the heater arrangement 604 includes the diode 606, which isconfigured/arranged to be reverse biased during the lasing state andforward biased during the non-lasing state for the laser diode 602.Thus, the heater arrangement 604 and circuit 600 are configured toprovide heating to the laser diode 602 during the non-lasing state andthe heater arrangement 604 is configured to warm the laser diodejunction to a temperature associated with a reduced risk of mode hoppingof the laser diode 602. The heater arrangement 604 can be controlled(e.g., through a pre-amp current driver) to maintain the temperature atthe junction within a predetermined temperature range.

Using the circuit 600 and components (e.g., diode 606 andheater/thermistor 608) of FIG. 6, the junction temperature can bemeasured during the non-lasing state. The junction temperature duringthe lasing state can be measured by another sensor (e.g. thermistor,photodiode, etc.), the heater/thermistor 608, and/or the diode 606 insome instances. Thus, the diode 606 can function as a temperature sensorin some embodiments. Junction temperature can be measured when the laserdiode 602 is in the lasing state and the non-lasing state. Based uponthe measured junction temperatures during the lasing state and thenon-lasing state, a drive signal can be applied to the heaterarrangement 604 to provide heating to the laser diode 602 during atleast the non-lasing state as the diode 606 is configured to be reversebiased during the lasing state and forward biased during the non-lasingstate.

FIG. 7 is a graph 700 of laser bias, V=[V_(a)=V_(b)], and laser junctiontemperature for the circuit 600 and components (e.g., laser diode 602)of FIG. 6 (indicated in FIG. 7 as “with heater”) as compared to acircuit and a laser diode that are not part of such an arrangement(indicated in FIG. 7 as “without heater”). As illustrated in FIG. 7,both arrangements (circuit with heater, and circuit without heater)operate with the same laser bias voltage and junction temperature duringa first laser on period 702. However, during a laser off period 704, theheater arrangement 604 (diode 606) is forward biased (e.g., providedwith negative bias from the laser perspective). During the initial timeperiod of the laser off period 704, the heater arrangement 604, with theheater/thermistor 608, acts in a thermistor mode 706 to measure thelaser temperature at the junction (in addition to providing heatingthereto). Thus, the heater/thermistor 608 serves as a temperature sensorfor the laser diode junction at least during a portion of the non-lasingstate. In some cases, sensing can be accomplished during a lower laserbias level than during heater mode 708, as illustrated in FIG. 7. One orboth of the thermistor mode 706 and the heater mode 708 may involveapplication of preheating to the junction during the laser off period704. When lasing is desired, the laser bias is driven in an opposingdirection such that the laser diode 602 is ready for lasing asillustrated by 710. Application of a higher forward bias voltage to thelaser diode causes the laser to lase in a laser on mode 712.

FIG. 7 additionally illustrates the difference between junctiontemperatures of a laser diode without heating and the laser diode 602with heating. As illustrated in FIG. 7, region 714 of the laser diode602 experiences a much smaller temperature fluctuation at the junctionthan the laser diode with no heater. Thus, ΔT₂<ΔT₁ (i.e. the temperaturedifferential ΔT₂ of the junction for the laser diode 602 between thelasing state and the non-lasing state is smaller than the temperaturedifferential ΔT₁ of the junction for the laser diode without a heaterbetween the lasing state and the non-lasing state).

FIG. 8 is a simplified circuit arrangement 800 that electrically couplesa laser diode 802 and a heater arrangement 804 in a parallelrelationship. FIG. 8 illustrates an embodiment in which current passingthrough the forward biased diode 806 provides sufficient heat generationfor the laser diode 802 during the non-lasing state, without need for anadditional heating element (e.g., resistor or thermistor). The circuitarrangement 800 and components are configured in the manner previouslydiscussed with regard to FIG. 6. The heater arrangement 804 of FIG. 8comprises a diode 806, which is configured to be reverse biased duringthe lasing state and forward biased during the non-lasing state for thelaser diode 802. The diode 806 can also act as a temperature sensor insome embodiments. Thus, the heating arrangement 804 can also be atemperature sensor. The circuit 800 is configured to alternately operatethe laser diode 802 in a lasing state and a non-lasing state, and toactivate the heater arrangement 804 (e.g. the diode 806) during thenon-lasing state to warm a junction of the laser diode 802.

In addition to providing heating to the laser diode junction during thenon-lasing state in some embodiments, the embodiments of FIGS. 6 and 8can also in some scenarios be used to activate the heater arrangement604, 804 during at least a portion of the non-lasing state and at leasta portion of the lasing state to warm the junction of the laser diode602, 802. FIG. 9 provides a graph 900 of such a scenario. FIG. 9 showslaser bias over time and illustrates an oscillating drive signal 902including a negative-going portion 904 for forward biasing the heaterarrangement 604, 804 to produce heat. In FIG. 9, the generated drivesignal 902 has an energizing portion 906 and a non-energizing portion908 that causes the laser diode 602, 802 to operate in the lasing stateand non-lasing state, respectively. As illustrated in FIG. 9, theenergizing portion 906 comprises part of the negative-going portion 904for forward biasing the heater arrangement 604, 804 (e.g. diode 606,806) during at least a portion of the lasing state. The drive signal 902can be viewed as having a first envelop 910 defined by the positiveamplitude peaks of the drive signal 902. The drive signal 902 can beviewed as having a second envelop 912 defined by the negative amplitudepeaks of the drive signal 902. The magnitude of the bias voltagedefining the first envelop 910 dictates whether the laser diode is inthe lasing or non-lasing state (laser on, laser off). The magnitude ofthe bias voltage defining the second envelop 912 dictates if and to whatextent the heater arrangement 604, 804 (e.g., diode 606, 806) isproducing heat. The drive signal 902 can be generated with a frequencyand amplitude profile sufficient to produce both lasing and heating asdesired. For example, one or both of the bias voltage magnitude andfrequency can be selected and adjusted to shape the negative-goingheating envelop of the drive signal to achieve a desired level of laserdiode heating during at least a portion of the lasing state and thenon-lasing state. Analysis indicates that HAMR recording can besuccessful if the frequency of laser diode bias is higher thanapproximately the half the drive data-rate. As a numerical example,consider a disc drive with data-rates on the order of 4 gigabits persecond. Thus, the minimum frequency for laser diode bias is expected tobe on the order of 2 GHz.

FIG. 10 is another simplified view of two circuits 1000 that areelectrically separated from one another yet allow for heat generated bycomponents electrically coupled to a first circuit 1000A to heatcomponents that are electrically coupled to a second circuit 1000B. Thesecond circuit 1000B allows a bias voltage (V_(a)−V_(b)) to be appliedto a laser diode 1002. The first circuit 1000A allows a second biasvoltage (V_(d)−V_(c)) to be applied to a heater arrangement 1004. Theheater arrangement 1004 can be disposed proximate the laser diode 1002as described previously and can be used to heat the laser diode 1002.Indeed, in some instances the spatial proximity of the heaterarrangement 1004 to the laser junction is such that heat can diffusequickly (e.g., <1 μs) to the laser junction and maintain a small laserjunction temperature variation. In the embodiment of FIG. 10, the heaterarrangement 1004 can comprise a diode 1006 coupled in series with aheater 1008. However, in some embodiments the heater arrangement 1004can comprise only a diode, or can comprise a heater/thermistor aspreviously discussed. In some instances, the diode 1006 can comprise aphotodiode arranged to facilitate power monitoring of the laser diode1002. The photodiode could provide heating of the laser diode during atleast the non-lasing state. The heater arrangement 1004 and the firstcircuit 1000A are configured to provide heating to the laser diode 1002as desired (e.g., during one or both of the non-lasing state and thelasing state). For example, the first circuit 1000A can be activatedduring the non-lasing state to heat the laser diode 1002, and during atleast an end portion of the lasing state to pre-heat the laser diode1002 and thereby reduce the junction temperature variation betweenlasing and non-lasing states. The heater arrangement 1004 can beconfigured to warm the laser diode junction to a temperature associatedwith a reduced risk of mode hopping of the laser diode 1002.Additionally, the heater arrangement 1004 can be controlled (e.g.,through a pre-amp current driver) to maintain the temperature at thejunction within a predetermined temperature range.

FIG. 11 illustrates an exemplary method that utilizes a circuit (e.g.600, 800, 1000, etc.) to measure a junction temperature of and heat alaser diode. The method measures 1101 the junction temperature of alaser diode in a lasing state that facilitates heat assisted recordingand in the non-lasing state. The method generates 1102 a drive signalhaving an energizing portion and a non-energizing portion to cause thelaser diode to operate in the lasing state and non-lasing state,respectively. The method activates 1103 a diode of a heater arrangementcoupled in parallel with the laser diode using at least thenon-energizing portion of the drive signal, and heats 1104 the laserdiode using the heater arrangement during at least the non-lasing state.In some cases, the energizing portion can comprise a negative-goingportion for forward biasing the diode during at least a portion of thelasing state and the heating of the laser diode can occur during atleast a portion of the lasing state. In some instances, the heaterarrangement can facilitate measurement of the junction temperature (i.e.act as a temperature sensor). The operation of the heater arrangementcan be controlled based upon the measured junction temperature. Heatingcan occur such that the junction temperature falls within a temperaturerange associated with a reduced risk of mode hopping of the laser diode.

FIGS. 12-14 are schematic views of apparatuses 1200, 1300, and 1400(e.g., HAMR apparatuses) and related components that can utilize heatingof a junction of a laser diode to reduce laser mode hopping according tovarious embodiments. FIGS. 12-14 show views of a HAMR configurationaccording to one example embodiment. In FIGS. 12-14, the configurationis a laser-on-slider (LOS) configuration. Other configurations, such asa laser-in-slider (LIS) configuration are contemplated. Indeed, theembodiments described may be applicable to a variety of energy deliveryconfigurations and laser diode types. In the LOS configuration, eachapparatus (slider) 1200, 1300, and 1400 includes a slider body 1201having an laser diode 1202 mounted to or otherwise disposed adjacent(e.g., with use of a submount) a first surface 1204 thereof. The laserdiode 1202 is proximate to a HAMR read/write element 1206, which has oneedge on an air bearing surface 1205 of the slider body 1201. The airbearing surface 1205 faces and is held proximate to a moving magneticrecording medium 1211 during device operation.

While here the read/write element 1206 is shown as a single unit, thistype of device may have a physically and electrically separate readelement (e.g., magnetoresistive stack) and write element (e.g., a writecoil and pole) that are located in the same general region of the sliderbody 1201. The separate read and write portion of the read/write element1206 may be separately controlled (e.g., having different signal lines,different head-to-media spacing control elements, etc.), although mayshare some common elements (e.g., common signal return path). It will beunderstood that the concepts described herein relative to the read/writeelement 1206 may be applicable to individual read or write portionsthereof, and may be also applicable where multiple ones of the readwrite portions are used, e.g., two or more read elements, two or morewrite elements, etc.

The laser diode 1202 provides electromagnetic energy to heat the mediasurface at a point near to the read/write element 1206. Optical pathcomponents, such as a waveguide 1210, can be formed integrally withinthe slider body 1201 to deliver light from the laser diode 1202 to themedium 1211. In particular, a local waveguide and NFT 1212 may belocated proximate the read/write element 1206 to provide local heatingof the media during write operations. The NFT is designed to supportlocal surface-plasmon at a designed light wavelength. At resonance, highelectric field surrounds the NFT due to the collective oscillation ofelectrons in the metal. Part of the field will tunnel into a storagemedium and get absorbed, raising the temperature of the medium locallyfor recording.

In FIG. 12, the apparatus 1200 can include one or more heaterarrangements 1216 configured to warm a junction of the laser diode. Theheater arrangement 1216 may be positioned proximate (e.g., adjacent) thelaser diode 1202 as illustrated or in other embodiments may be disposedwithin or along the laser diode itself. In FIG. 12, an analyzer 1217(e.g., a processor) is illustrated communicating with a controller 1218.The analyzer 1217 can be configured to determine a temperature of thelaser diode junction in some instances. Additionally, the analyzer 1217can determine laser diode power output (e.g., from a photodiode), andcompare junction temperature and an injection current supplied duringthe lasing state to stored combinations of junction temperature andinjection current to determine a likelihood of mode hopping occurringfor the laser diode during the lasing state. The controller 1218 cancommunicate with the analyzer and can be configured to vary the currentsupplied to the heater arrangement for varying a temperature of thejunction to reduce the likelihood of mode hopping occurring during thelasing state.

FIG. 12 shows an arrangement where the laser diode 1202 and heaterarrangement 1216 are controlled together. Thus, the controller 1218 canbe coupled to both the heater arrangement 1216 and the laser diode 1202to control lasing and to control when the heater arrangement 1216 is onrelative to the non-lasing state (and/or the lasing state). Optionally,or in addition, the controller 1218 can be used to control an amount ofinjection current (power) applied to one or both of the heaterarrangement 1216 and the laser diode 1102 to vary a temperature of thejunction.

The controller 1218 can include a write control module 1220 thatcontrols various aspects of the device during write operations. For aHAMR device, writing involves activating the laser diode 1202 whilewriting to the media, which is indicated by way of laser and heatercontrol module 1221. The laser and heater control module 1221 includescircuitry that switches the laser diode 1202 on and off, e.g., inresponse to a command from write control module 1220. In someembodiments, the laser and heater control 1224 can switch the heaterarrangement 1216 on and off inversely to the laser diode 1202 to warmthe junction of the laser diode 1202 as discussed with reference toFIGS. 6, 8, and 10. In other embodiments, the laser and heater control1224 can activate the heating arrangement during at least a portion ofthe non-lasing state and at least a portion of the lasing state to warmthe junction of the laser diode as discussed with reference to FIGS. 6,8, and 10.

FIG. 13 illustrates an embodiment with a controller 1318 coupled to boththe heater arrangement 1216 and the laser diode 1202 to control lasingand to control when the heater arrangement 1216 is on relative to thenon-lasing state (and/or the lasing state). The controller 1318 can becoupled to the analyzer 1217, which provides for monitoring as discussedpreviously. The embodiment of FIG. 13 has a separate laser control 1322in addition to a heater control 1324. The laser control 1322 and theheater control 1324 can be used to activate the heater arrangement 1216during (a) the non-lasing state or (b) at least a portion of thenon-lasing state and at least a portion of the lasing state to warm thejunction of the laser diode 1202.

FIG. 14 illustrates yet another embodiment with a controller 1418coupled to both the heater arrangement 1216 and the laser diode 1202 tocontrol lasing and to control when the heater arrangement 1216 is onrelative to the non-lasing state (and/or the lasing state). Thecontroller 1418 can be coupled to the analyzer 1217, which provides formonitoring as discussed previously. FIG. 14 has a laser control 1422 anda heater control 1424. Although illustrated as two separate modules inFIG. 14, in some embodiments the laser control 1422 and the heatercontrol 1424 can be combined. The heater control 1424 can be coupled toa laser power monitor 1425 (e.g., a photodiode) disposed proximate thelaser diode 1202 to allow for monitoring of the junction. In someinstances, the laser power monitor 1425 can optionally be disposedsufficiently close to the laser diode 1202 and be configured to warm thejunction, and thereby reduce the likelihood of mode hopping. Thus, thelaser control 1422 and the heater control 1424 can used to activate thelaser power monitor 1425 to provide heating during (a) the non-lasingstate or (b) at least a portion of the non-lasing state and at least aportion of the lasing state to warm the junction of the laser diode1202.

The foregoing description of the example embodiments has been presentedfor the purposes of illustration and description. It is not intended tobe exhaustive or to limit the embodiments to the precise form disclosed.Many modifications and variations are possible in light of the aboveteaching. Any or all features of the disclosed embodiments can beapplied individually or in any combination are not meant to be limiting,but purely illustrative. It is intended that the scope of the inventionbe limited not with this detailed description, but rather determined bythe claims appended hereto.

What is claimed is:
 1. A method, comprising: operating a laser diode ina lasing state to facilitate heat-assisted magnetic recording;determining a voltage differential between a transient voltage lasingstate of the laser diode and a constant voltage lasing state of thelaser diode; determining, using the voltage differential, a temperatureat a junction of the laser diode when the laser diode is operated in thelasing state; comparing the junction temperature and an injectioncurrent supplied to the laser diode during the lasing state to storedcombinations of junction temperature and injection current; and avoidinga combination of junction temperature and injection current for whichmode hopping is likely to occur during the lasing state.
 2. The methodof claim 1, wherein the junction temperature is determined using thevoltage differential and a proportionality factor.
 3. The method ofclaim 2, wherein the proportionality factor (K) is characterized byK=(V₁−V₂)/(T₂−T₁), where V₁ is a voltage measured during a first state,V₂ is a voltage measured during a second state, T₂ is a temperaturemeasured during the second state, and T₁ is a temperature measuredduring the first state.
 4. The method of claim 1, wherein determiningthe voltage differential comprises determining a difference in forwardvoltage of the laser diode measured before and after applying a pulseddrive current to the laser diode during the lasing state.
 5. The methodof claim 1, wherein avoiding comprises adjusting the injection currentto avoid the combination of junction temperature and injection currentfor which mode hopping is likely to occur during the lasing state. 6.The method of claim 1, wherein avoiding comprises heating or cooling thelaser diode to avoid the combination of junction temperature andinjection current for which mode hopping is likely to occur during thelasing state.
 7. The method of claim 1, wherein avoiding comprisespreheating the laser diode prior to writing data to avoid thecombination of junction temperature and injection current for which modehopping is likely to occur during the lasing state.
 8. The method ofclaim 1, wherein avoiding comprising heating the laser diode during anon-lasing state.
 9. The method of claim 1, wherein avoiding comprisesheating the laser diode during at least a portion of the lasing stateand a non-lasing state.
 10. A method, comprising: operating a laserdiode in a lasing state to facilitate heat-assisted magnetic recording;determining a voltage differential between a transient voltage lasingstate of the laser diode and a constant voltage lasing state of thelaser diode; and determining, using the voltage differential, atemperature at a junction of the laser diode when the laser diode isoperated in the lasing state.
 11. The method of claim 10, wherein thejunction temperature is determined using the voltage differential and aproportionality factor.
 12. The method of claim 11, wherein theproportionality factor (K) is characterized by K=(V₁−V₂)/(T₂−T₁), whereV₁ is a voltage measured during a first state, V₂ is a voltage measuredduring a second state, T₂ is a temperature measured during the secondstate, and T₁ is a temperature measured during the first state.
 13. Themethod of claim 10, wherein determining the voltage differentialcomprises determining a difference in forward voltage of the laser diodemeasured before and after applying a pulsed drive current to the laserdiode during the lasing state.
 14. An apparatus, comprising: a sliderconfigured for heat-assisted magnetic recording, the slider comprising alaser diode; a controller configured to calculate a voltage differentialbetween a transient voltage lasing state of the laser diode and aconstant voltage lasing state of the laser diode, the controller furtherconfigured to determine, using the voltage differential, a temperatureat a junction of the laser diode when the laser diode is operated in thelasing state; and a processor configured to compare the junctiontemperature and an injection current supplied to the laser diode duringthe lasing state to stored combinations of junction temperature andinjection current, the processor further configured to avoid acombination of junction temperature and injection current for which modehopping is likely to occur during the lasing state.
 15. The apparatus ofclaim 14, wherein the controller is configured to determine the junctiontemperature using the voltage differential and a proportionality factor.16. The apparatus of claim 15, wherein the proportionality factor (K) ischaracterized by K=(V₁−V₂)/(T₂−T₁), where V₁ is a voltage measuredduring a first state, V₂ is a voltage measured during a second state, T₂is a temperature measured during the second state, and T₁ is atemperature measured during the first state.
 17. The apparatus of claim14, wherein the controller is configured to determine the voltagedifferential by determining a difference in forward voltage of the laserdiode measured before and after application of a pulsed drive current tothe laser diode during the lasing state.
 18. The apparatus of claim 14,further comprising a heater arrangement proximate the laser diode;wherein the controller is configured to activate the heater arrangementto warm the junction and maintain the junction temperature within apredetermined temperature range associated with a reduced likelihood ofmode hopping occurring for the laser diode during the lasing state. 19.The apparatus of claim 18, wherein the heater arrangement is coupled ina parallel relationship with the laser diode, and wherein the heaterarrangement comprises one or more of a diode, a diode arranged in serieswith a thermistor, and a diode arranged in series with a heater.
 20. Theapparatus of claim 14, wherein the controller is configured to modifyone or more of an injection current, a laser diode power, and a headposition relative to a magnetic recording medium to compensate for alaser diode power variation due to mode hopping.